The Collaborative International Dictionary of English v.0.48:

Newcastle \New"cast`le\, prop. n.
   A town in England.
   [PJC]

   Carry coals to Newcastle to do something utterly
      superfluous; to do something useless or wasteful; -- from
      the nearness of Newcastle to the coal-mining district.
      [PJC]

WordNet (r) 3.0 (2006):

Newcastle
    n 1: a port city in northeastern England on the River Tyne; a
         center for coal exports (giving rise to the expression
         `carry coals to Newcastle' meaning to do something
         unnecessary) [syn: Newcastle, Newcastle-upon-Tyne]

U.S. Gazetteer Places (2000):

Newcastle, WY -- U.S. city in Wyoming
   Population (2000):    3065
   Housing Units (2000): 1458
   Land area (2000):     2.467594 sq. miles (6.391040 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    2.467594 sq. miles (6.391040 sq. km)
   FIPS code:            56215
   Located within:       Wyoming (WY), FIPS 56
   Location:             43.853183 N, 104.209343 W
   ZIP Codes (1990):     82701
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Newcastle, WY
    Newcastle


U.S. Gazetteer Places (2000):

Newcastle, NE -- U.S. village in Nebraska
   Population (2000):    299
   Housing Units (2000): 153
   Land area (2000):     0.335003 sq. miles (0.867655 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.335003 sq. miles (0.867655 sq. km)
   FIPS code:            34090
   Located within:       Nebraska (NE), FIPS 31
   Location:             42.652005 N, 96.875265 W
   ZIP Codes (1990):     68757
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Newcastle, NE
    Newcastle


U.S. Gazetteer Places (2000):

Newcastle, OK -- U.S. city in Oklahoma
   Population (2000):    5434
   Housing Units (2000): 2071
   Land area (2000):     49.758871 sq. miles (128.874878 sq. km)
   Water area (2000):    3.180307 sq. miles (8.236956 sq. km)
   Total area (2000):    52.939178 sq. miles (137.111834 sq. km)
   FIPS code:            51150
   Located within:       Oklahoma (OK), FIPS 40
   Location:             35.240224 N, 97.591398 W
   ZIP Codes (1990):     73065
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Newcastle, OK
    Newcastle


U.S. Gazetteer Places (2000):

Newcastle, TX -- U.S. city in Texas
   Population (2000):    575
   Housing Units (2000): 266
   Land area (2000):     1.811203 sq. miles (4.690993 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    1.811203 sq. miles (4.690993 sq. km)
   FIPS code:            50868
   Located within:       Texas (TX), FIPS 48
   Location:             33.192383 N, 98.737969 W
   ZIP Codes (1990):     76372
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Newcastle, TX
    Newcastle


U.S. Gazetteer Places (2000):

Newcastle, WA -- U.S. city in Washington
   Population (2000):    7737
   Housing Units (2000): 3117
   Land area (2000):     4.468332 sq. miles (11.572925 sq. km)
   Water area (2000):    0.011119 sq. miles (0.028799 sq. km)
   Total area (2000):    4.479451 sq. miles (11.601724 sq. km)
   FIPS code:            48645
   Located within:       Washington (WA), FIPS 53
   Location:             47.533215 N, 122.172101 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Newcastle, WA
    Newcastle